Life History Strategy and Ecosystem Impact of a Dominant Small Mammal Herbivore in a Mountain Steppe
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Life history strategy and ecosystem impact of a dominant small mammal herbivore in a mountain steppe Karin Nadrowski 12th April 2006 Contents Acknowledgements . vii Abstract . viii Zusammenfassung . x 1 Introduction 1 1.1 Mountain steppe . 1 1.2 Herbivores . 2 1.3 Life history strategies . 3 1.4 From keystone species to small mammal pest: Ecosystem impacts . 4 1.5 Situation in Mongolia and project background . 7 1.6 Aim of this study . 8 2 Basic Data Collection 13 2.1 Study area . 13 2.1.1 Climate . 14 2.1.2 Soils . 16 2.1.3 Vegetation . 16 2.1.4 Higher trophic level . 18 2.2 Life history strategies of pikas . 19 2.3 Pikas found in the study area . 25 2.4 Grid trapping and observation . 26 2.4.1 Capture site and burrow characteristics . 26 2.4.2 Capture . 28 2.4.3 Observation . 30 2.4.4 Captured species and biomass of small mammals . 30 2.4.5 Welfare considerations in trapping and handling pikas . 32 2.4.6 Capture and observation success . 34 2.4.7 To trap or not to trap? Comparing trapping with observation . 35 2.5 Parasites . 40 2.6 Movement . 42 2.7 Summary . 46 3 Estimating Density 47 3.1 Introduction . 47 3.2 Methods . 48 3.3 Results . 51 3.4 Discussion . 52 3.5 Summary . 55 i CONTENTS 4 Life history 57 4.1 Age structure and life tables . 57 4.1.1 From weight to age . 58 4.1.2 Seasonal development of age structure . 69 4.1.3 Cohort life tables . 74 4.1.4 Summary . 78 4.2 Modelling survival rates . 79 4.2.1 Modelling background . 79 4.2.2 Survival rates . 81 4.2.3 Survival of early and late litter . 92 4.2.4 Summary . 94 4.3 Reproduction . 96 4.4 Population dynamics . 99 4.5 Discussing life history strategy . 101 4.6 Summary . 108 5 Ecosystem impact 109 5.1 Production and biomass removal . 109 5.2 Pika densities on regional scale . 124 5.3 Summary . 131 6 General Discussion 133 6.1 Life history strategy . 133 6.2 Ecosystem impact . 137 6.3 Further research needs . 141 References 143 Curriculum vitae 155 ii List of Figures 2.1 Location of the Gobi Gurvan Saikhan National Conservation Park . 14 2.2 Map of the study area comprising the Duund and Zuun Saikhan . 14 2.3 Picture on the south facing slope of the Duund Saikhan . 15 2.4 Picture of the research camp . 16 2.5 Walther-Lieth diagrams of two climatic stations within the park . 16 2.6 Gradient of soil profiles along an altitudinal transect . 17 2.7 Picture of burrow sampling plots . 18 2.8 Picture of the Mongolian and the Daurian pika . 21 2.9 Distribution of the Daurian pika . 21 2.10 Distribution of the Pallas pika . 22 2.11 Map of burrows and trap locations on the trapping site . 27 2.12 Mongolian pikas encountered by capture or observation . 36 2.13 Parasite load during the year . 41 2.14 Movement distances within two years . 43 2.15 Movement distances within and between sample sessions . 44 3.1 Density estimates . 53 4.1 Weight structure of captured pikas . 60 4.2 Average weight determined by growth curves . 62 4.3 Growth curve from maximum growth rates . 63 4.4 Discriminating juveniles from adults . 64 4.5 Predictions for age class composition . 65 4.6 Comparing growth of O. pallasi pricei, rufescens, curzoniae . 67 4.7 Cohort survival based on capture and observation . 70 4.8 Cohort survival based on capture . 70 4.9 Cohort survival based on capture for three summers . 71 4.10 Probabilities for two encounter histories . 79 4.11 Survival rates depending on density, sex, and age . 88 4.12 Survival rates for individuals from early and late litter . 95 4.13 Reproductive state during the year . 97 4.14 Trajectories for the numbers of males over females . 101 4.15 Two pikas fighting over territories . 101 5.1 Hierarchical design of the exclosure experiment . 112 5.2 Estimates for standing crop based on habitat, time, and pika grazing . 115 5.3 Estimates for standing crop predicted by species group . 119 5.4 Pika burrow densities for different livestock densities and altitudes . 127 iii LIST OF FIGURES iv List of Tables 2.1 Precipitation in the summer months from 2000 to 2003 . 15 2.2 Standing crop along an altitudinal transect . 17 2.3 Rare and endangered animal species in the GGS . 18 2.4 Life history traits of Ochotona daurica and O. pallasi . 24 2.5 Habitat preference of Ochotona pallasi pricei and O. daurica . 26 2.6 Date, duration, and reference area of sample sessions . 29 2.7 Species captured on the trapping site . 31 2.8 Ochotona pallasi pricei captured and observed on the trapping site . 34 2.9 Accuracy of identification by capture and observation . 37 2.10 Length and regularity of encounters by capture and observation . 38 2.11 Information gained by additional observation . 39 2.12 Information gained by additional capture . 40 3.1 Abundance and density predicted by different estimators . 50 3.2 Movement distances based on capture and observation . 52 4.1 Median weights for all capture sessions . 61 4.2 Individuals used to construct a growth curve for maximum growth rate 63 4.3 Predicted cohort strengths based on winter and growth criteria . 64 4.4 Age structure at the end of the summers 2000-2002 . 71 4.5 Cohort Life Tables . 75 4.6 Life Tables for all sexes . 76 4.7 Life Tables for litter . 77 4.8 Propabilities to observe four different encounter occasions . 80 4.9 Number of animals used for modelling . 82 4.10 Parameter coding for pooled data, using the most reliable information . 83 4.11 Parameter coding for capture data, spanning three summers . 84 4.12 Candidate models set . 85 4.13 Model likelihoods for recapture, pooled data . 86 4.14 Model likelihoods for survival, pooled data . 87 4.15 Model likelihoods for recapture, capture data . 89 4.16 Model likelihoods for survival, capture data . 90 4.17 Canditate models set for individuals from early and late litter . 93 4.18 Model likelihoods for early and late litter . 94 4.19 Pika life history traits revisited . 102 5.1 Number of pikas captured in the summers from 2001 to 2003 . 110 5.2 Plant species cover on sample plots . 111 v LIST OF TABLES 5.3 Precipitation in the summers of 2002 and 2003 . 111 5.4 Analysis of variance table for standing crop comparing two summers . 114 5.5 Analysis of variance table for standing crop comparing species groups . 116 5.6 Significant effects from the ANOVA for species groups . 120 5.7 Production and biomass removal for a mountain steppe with burrows . 121 5.8 Ratio of burrow to steppe productivity along an altitudinal transect . 125 5.9 Production and biomass removal along an altitudinal transect . 128 vi Acknowledgements This project could never have been finished without the help of many people, friends and advisors and anything in between. Thank you for helping, fighting, growing, loving, enduring and encouraging me in so many various ways! I am grateful to Prof. Dr. G. Miehe, Prof. Dr. R. Samjaa, Prof. Dr. R. Brandl, Dr. V. Re- tzer, Dr. K. Wesche, Dr. J. Dauber, T. Monkhzul, R. Klug, Devlin, Carola, and Bettina for giving scientific advice and encouragement. V. Retzer, K. Wesche, S. Jansen, G. Miehe, V. Clausnitzer, T. Monkhzul, R. Undrakh, Enkhjargal, Bjambaa, Bekhee, S. Schmidt, Enkhshimek, Ojuntsetseg, Shurentsetseg, K. and E.-O. Nadrowski and many others gave invaluable help during the organisation of this project. Thank you Vroni, Vayu, Ria, Lou, Gouine, Frank, Sandra, Thomas, Christina, Tatjana, HikE, Monkhzul, Janis, Bj¨orn, Maike und Ines for your friendship and love. Thanks go to the staff of the Faculty of Geography of the Philipps-University of Mar- burg, the working-group of animal ecology in the Faculty of Biology of the University in Marburg, the staff of the Faculty of Biology of the Mongolian University, the staff of the GTZ-office in Mongolia, and the staff of the Research Center for Infectious Diseases in Dalandzadgad. The German Acadamic exchange, the German Science Foundation, and the Ministry of Economic Co-operation funded this project..